The present invention relates generally to a vortex-flow hydraulic shock absorber for damping relative displacement of two components, such as a vehicle body and a vehicle wheel. More particularly, the invention relates to a vortex-flow shock absorber in which the damping force varys depending upon a piston stroke and a piston speed.
Published British Patent Application No. 2044882 disclosed a vortex-flow shock absorber with a piston having a chamber through which the working fluid flows in vortex fashion to produce the damping force. The published British application discloses a piston partitioned to have two chambers for producing vortex fluid flow during both the expansion and compression strokes of the piston.
In a vehicle suspension, the shock absorber is required to create a substantially small damping force against a road shock which causes substantially a small piston stroke and to create a large damping force against a cornering force which causes a large piston stroke. A relatively small damping force against the road shock provides the vehicle satisfactory riding comfort. On the other hand, a relatively large damping force against the cornering force may provide driving stability. To provide such piston stroke dependent damping force variable shock absorber, Published European Patent Application No. 0053378 discloses a piston stroke responsive vortex-flow shock absorber in which a variable damping force is created independent of the piston stroke and piston speed. The piston has a valve which is responsive to the pressure difference between the upper and lower fluid chambers of the shock absorber to relieve the fluid pressure in the higher pressure chamber to the lower pressure chamber when the pressure difference exceeds a predetermined set pressure.
The present invention is an improved vortex-flow shock absorber which achieves better shock absorbing characteristics.